[Collins] KWM-2a has no low audio on SSB output on 75 meters.

[Cam and Juli Hedrick]

HI all, 
Where do I start, I was on 75 meters tonight and the report of my audio was
shocking? It has a hum and the low end of the audio is flat.  All is well on
40, 30, 20, 17, 15, and 10 meters when I looked at it on the spectrum
analyzer into a dummy load, but 80 and 75 looks yucky.
Output is also lower by 50 watts on 75 meters, I get 110 watts everywhere
else.  I guess I need to put it on the bench and align it, plus test the
audio output tube in the mixer.
Any advice before I start?
Cam
WA4JKW